1. Field of the Invention
The present invention relates to a motor drive apparatus with a function to detect an abnormality in a power device.
2. Description of the Related Art
In motor drive apparatuses for driving motors in machine tools, forming machinery, molding machines, industrial machinery, or various robots, AC power supplied by an AC power source is converted to DC power by a converter and then converted to AC power by an inverter, and this AC power is used as drive power for motors respectively provided for drive axes. The inverter includes a bridge circuit constituting a switch unit having a power device (semiconductor switching device) and a diode in antiparallel connection thereto and converts DC power to AC power and outputs the AC power by tuning on and off the power device.
When a current passes through a power device, the device heats up and excessive heating would lead to an abnormality such as a breakdown of the power device. To detect an abnormality in a power device, it is preferable to use a temperature sensor, but it is difficult to mount a temperature sensor directly on the semiconductor chip of a power device.
As a technique known for detecting the temperature of a power device without providing a separate temperature sensor, for example, Japanese Unexamined Patent Publication (Kokai) No. 2002-289856 discloses an on-chip temperature detection device including: a current-controlled semiconductor device including a base terminal, a collector terminal, an emitter terminal, and a diode based on p-n junction between the base terminal and the emitter terminal; first means for allowing a certain base current to pass through the base terminal when the control signal applied to the base terminal is off, the certain base current being smaller than a base current that would switch the current-controlled semiconductor device to the normal ON state; second means for detecting a temperature of the current-controlled semiconductor device on the basis of a forward voltage between the base and the emitter of the current-controlled semiconductor device when the certain base current smaller than a base current that would switch the current-controlled semiconductor device to the normal ON state passes the base terminal, wherein the detection of the temperature is conducted based on temperature dependence of the forward voltage of the diode based on p-n junction in the OFF state of the current-controlled semiconductor device.